Place the chicken breasts on a cutting board and cover with a large sheet of plastic wrap. With a rolling pin, meat mallet, or your palm, lightly pound into an even thickness.
To Dry Brine*: Place the chicken on a plate and sprinkle all over with the kosher salt. Place in the refrigerator uncovered for at least 30 minutes or up to 1 day—if you will not be dry brining, skip this step.
When ready to air fry: remove the chicken from the refrigerator and let stand at room temperature for 15 minutes.
In a small bowl, stir together the paprika, garlic powder, onion powder, and black pepper (if you did not dry brine the chicken, add the salt now)
Place the chicken in a large bowl and drizzle with the olive oil. Sprinkle the spice mixture over the top. Toss to coat the chicken, ensuring you rub the spices evenly over both sides.
Preheat the air fryer to 375 degrees F (my model takes 3 minutes to heat). Place the chicken presentation side (smooth side) down in the air fryer and let cook 6 minutes.
Remove the air fryer basket, then with tongs, carefully flip the chicken over. Continue cooking until the chicken registers between 155 and 160 degrees F, 2 to 8 minutes more. Chicken is considered safe to eat at 165 degrees F, but I like to remove mine a few degrees early, then let the carryover cooking finish the job. The total cook time will vary based on your model and the size of your chicken. Smaller breasts (about 6 ounces each) will need only around 8 minutes total; larger ones may need 14 or more. Check the chicken often towards the end to monitor its progress. DO NOT overcook or it will be dry.
Remove the chicken to a plate. Cover and let rest 5 to 10 minutes. Slice and enjoy!
*While dry brining isn't 100% mandatory (the spices, cooking temperature, and cook times listed in this recipe are still correct for the best air fryer chicken breasts), brining works magic on meat. It improves its texture (it makes it juicy, plump, and meaty, not rubbery) and its flavor, because the meat will taste more seasoned all the way through, not just on the outside. If you have time for brining, I highly recommend it.